It is required of an electrophotographic toner binder for a heat fixing method adopted generally as a fixing method of an image in a copier, a printer, and the like that a toner does not fuse with a heat roll even at a high fixing temperature (hot offset resistance); that a toner can be fixed even at a low fixing temperature (low temperature fixing properties); that storage stability as fine particles is good (blocking resistance); and the like.
In order to improve such fixing performance of a toner, there is conventionally known a method in which incompatible resins specialized in a low temperature range and a high temperature range respectively are used as a matrix phase and a domain phase. In addition, there is proposed a method in which a compatibilizing agent for compatibilizing the incompatible resins is contained in a vinyl resin such as a styrene polymer (Patent Document 1, etc.).
In order to improve blocking resistance, especially blocking resistance in relation to storage stability under a high temperature and high humidity environment, there is proposed a toner binder composed of a polyester resin obtained by using a specific polyol component such as 1,2-propylene glycol and neopentyl glycol, without consideration for the SP value range and the HLB value range (Patent Document 2, etc.).